This invention relates to a gas circuit breaker including a suction chamber adapted to generate negative pressure and a pressure chamber adapted to temporarily reserve an arc extinguishing gas which is raised in pressure due to arc energy.
A typical gas circuit breaker of a prior art construction is as shown in FIGS. 1 and 2. In the drawings, designated at reference numeral 1 is a fixed terminal plate, 2 is a fixed outer cylinder having one end thereof rigidly secured to the terminal plate 1 and the other end thereof secured to an insulating nozzle 3 and an insulating fixed piston 4 in the form of a "C" in section. A fixed arc contact 5 is rigidly secured to the terminal plate 1. A movable arc contact 6, which may be brought into contact with or released from the fixed arc contact 5, is coupled to a driving mechanism (not shown) and serves to conduct electric current through the terminal plate 1. A cylinder 7 formed of a conductive material and rigidly secured to the movable arc contact 6 is positioned adjacent the insulating fixed piston 4, which is rigidly secured to the fixed outer cylinder 2, the cylinder 7 also serving as a movable main contact for conducting electric current.
A fixed main contact 8 has one end thereof rigidly secured to the terminal plate 1 and the other end thereof in slidable contact with the movable main contact 7 to conduct the electric current. A main fixed contact 9 on the load side corresponds to the main fixed contact 8 on the power supply side, the former contact having one end thereof rigidly secured to a terminal plate 10 on the load side, which faces the terminal plate 1 on the power supply side. The other end thereof is in slidable contact with the movable main contact 7 to pass an electric current.
A bearing 11 is rigidly secured to the terminal plate 10 for supporting the movable arc contact 6. A pressure chamber 12 is defined by the terminal plate 1, the fixed outer cylinder 2, the insulated nozzle 3, the fixed arc contact 5 and the movable arc contact 6 in the closed state, and is adapted to contain an arc extinguishing fluid such as SF .sub.6 gas therein. On the other hand, a suction chamber 13 is defined by the fixed outer cylinder 2, the nozzle 3, the insulating fixed piston 4, the movable arc contact 6 and the cylinder (movable main contact) 7.
The aforesaid fixed contact 8 is disposed concentrically with the terminal plates 1 and 10, the fixed outer cylinder 2 and the other parts, similarly to the fixed main contact 9, so that the centers thereof locate on the same axis. The movable arc contact 6, shaped into the form of a shaft, is supported by the bearing 11 rigidly secured to the center of the terminal plate 10, and extends through the terminal plate 10, to be coupled to the driving mechanism. At numeral 12 is the pressure chamber. As mentioned above, 13 denotes a suction chamber, and a further chamber 14 is defined by the cylinder 7 and the fixed main contact 9. A ventilating hole 15 allows the chamber 14 and a container (not shown) filled with the arc extinguishing fluid to communicate with one another, and a guide hole 16 in the form of a cone allows the pressure chamber 12 and the suction chamber 13 to communicate with each other when the arc contacts are opened. Numeral 17 (FIG. 2) represents the arc generated when the breaker is opened, the arc occurring in an arc generating space 18. A ventilating hole 19 allows the pressure chamber 12 and a container (not shown) to communicate with one another, and a ventilating path 20 allows the suction chamber 13 to communicate with a container (not shown).
The manner of operation of the device will now be described. FIG. 1 shows the gas circuit breaker in the closed state, in which an electric current passes from the terminal plate 1 on the power supply side to the terminal plate 10 through the fixed main contact 8, the movable main contact 7 and the fixed main contact 9. A part of the electric current is shunted via a path starting at the terminal plate 1 and ending at the terminal plate 10, through the fixed arc contact 5 and the movable arc contact 6, the movable main contact 7 and the fixed main contact 9.
When a command to open the breaker is directed to the driving mechanism, the movable arc contact 6 moves in the direction indicated by an arrow a in FIG. 2, and withdraws by a predetermined distance. During this movement, the movable main contact 7 is first released from the fixed main contact 8 and then the movable arc contact 6 is released from the fixed arc contact 5 after a lapse of a predetermined time, so that the arc 17 is generated between the arc contacts 5, 6 (FIG. 2). On this occasion, the movable cylinder 7 rigidly secured to the movable arc contact 6 is moved leftward in the drawing while slidably contacting the insulating fixed piston 4. This withdrawal increases the capacity of the suction chamber 13, whereupon the fluid pressure within the suction chamber 13 is lowered, while the fluid pressure within the pressure chamber 12 is raised because of thermal emission. The movable arc contact 6 is further moved leftward. When the distal end (contact end) of the contact 6 has passed through the guide hole 16 formed by the insulated nozzle 3 and hence out of the pressure chamber, the suction and pressure chambers communicate with each other via the guide hole and the arc generating space 18, as illustrated in FIG. 2. A high-temperature, high-velocity fluid within the pressure chamber thus flows into the suction chamber through the arc generating space and the guide hole 16 as indicated by arrows b, and also a part of the fluid is discharged through the ventilating hole 19 formed in the terminal plate 1 into a fluid filling container (not shown) as indicated by arrow c. As it flows from the pressure chamber into the suction chamber, the fluid cools the arc 17 in the guide hole 16, so that the electric current is cut off at the point where the current becomes zero and the breaker assumes the state illustrated in FIG. 2. In the state, the fluid is discharged into the fluid filling container through the ventilating path 20 formed between the movable cylinder 7 and the fixed piston 4, as indicated by arrows d, due to high temperature in the suction chamber 13, so that there is secured insulation between the fixed arc contact 5 and the movable arc contact 6 and cut-off of the current is completed.
There will be now described the cut-off of a small current where the fluid pressure within the pressure chamber is not sufficiently raised. When the suction chamber is increased in capacity and the fluid pressure within the suction chamber is lowered upon the withdrawal of the movable arc contact 6 as shown in FIG. 2, a low-temperature, high-insulating fluid flows into the suction chamber 13 from a fluid filling container (not shown) through the ventilating hole formed in the terminal plate 1, while crossing the arc 17, as indicated by arrow c.sub.1. Due to the introduced fluid crossing the arc 17 in the guide hole 16, the arc 17 is cooled and hence the electric current is cut off at the point where the current becomes zero. A conductive fluid generated by the contact of the introduced fluid with the arc 17 is discharged into the fluid filling container through the ventilating path 20 as indicated by the arrows d, so that there is secured insulation between the fixed arc contact 5 and the movable arc contact 6; and cut-off of the relatively small current is completed.